Look up the thread about 100% Nitrox.... that should clear it all up.
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I'm guessing here, but I think it goes back to the fact that Nitrox is a specialty certification, not a "level".
I don't think it actually matters mgmonk. I just checked out my c-cards and they are exactly the same. Both AOW c-card and the Nitrox certification. I don't know... I tend to believe that PADI changes its card designs from time to time that's all. Plus they both write OWSI in front of my instructor's number...
DevonDiver: Holy light-sabres Luke. We need to re-certify as members of the Force (with the correct number and letter designations on our cert cards).